<!DOCTYPE html>
<html>
<head>
	<title></title>
</head>
<body>
<script type="text/javascript">
	// if适合判断范围
	
	// 90分案例
	let score = 77;
	if (score > 90) {
		console.log('a')
	} else if (score > 80) {
		console.log('b')
	} else if (score > 60) {
		console.log('c')
	} else if (score > 50) {
		console.log('d')
	}

	// 判断闰年
	let year = 1900;
	if (year % 4 && !(year % 100) || year % 400) {
		console.log('不是闰年');
	} else {
		console.log('闰年');
	}

</script>
</body>
</html>